1. Technical Field
The present invention relates to a light emitting device, a method of manufacturing the light emitting device, and an electronic apparatus having the light emitting device.
2. Related Art
In recent years, needs for flat panel display devices with small power consumption and weight have been increased with diversification of information instruments. As one of such flat panel display devices, an organic EL (Electroluminescence) device having a light emitting layer is known. Such an organic EL device generally has a configuration that a light emitting layer is disposed between a positive electrode and a negative electrode. In order to improve a hole injection ability or an electron injection ability, a configuration that a hole injecting layer is disposed between the positive electrode and the light emitting layer or a configuration that an electron injecting layer is disposed between the light emitting layer and a negative electrode has been suggested.
Materials used for a light emitting layer, a hole injecting layer, and an electron injecting layer of the organic EL device are often deteriorated through reaction with moisture in the air. The deterioration of the layers forms a light non-emitting area, which is referred to as a dark spot, in the organic EL device, thereby shortening the lifetime as a light emitting device. Therefore, such an organic EL device requires that influence by moisture or oxygen should be suppressed.
In order to solve such a problem, a technique of preventing invasion of moisture or oxygen by bonding a seal member made of glass or metal to a substrate of the organic EL device has generally been employed. However, with increase in size and decrease in thickness and weight of displays, it is difficult to prevent the invasion of moisture or oxygen only by the use of the bonded seal member. In order to satisfactorily secure areas for forming driving elements or wires with increase in size, needs for a top emission structure in which light is taken out from the seal member haven been suggested. For the purpose of accomplishing such requirement, a sealing structure using a transparent thin film with small weight and high strength has been required.
Therefore, in recent years, in order to cope with increase in size and decrease in thickness of display devices, techniques, which are referred to as thin film sealing, of forming a thin film made of silicon nitride, silicon oxide, and ceramics having a light transmitting property and an excellent gas barrier property as a gas barrier layer on a light emitting element by the use of a high density plasma method (for example, a ion plating method, an ECR plasma sputtering method, an ECR plasma CVD method, a surface wave plasma CVD method, an ICP-CVD method, or the like) have been used (for example, see JP-A-9-185994, JP-A-2001-284041, JP-A-2000-223264, and JP-A-2003-17244). According to such techniques, it is possible to prevent the invasion of moisture into the light emitting elements.
However, even by using such techniques, it is not possible to completely prevent the invasion of moisture from the outside, thereby not obtaining sufficient emission characteristic or emission lifetime. Specifically, detachment or crack is generated in outer circumferential portions or stepped portions of the gas barrier layer and thus the invasion of moisture through the detachment or crack is detected.
For this reason, it is considered that the generation of crack in the gas barrier layer is prevented by disposing an organic buffer layer having an approximately flat top surface below the gas barrier layer. That is, stress generated due to the warping or volume expansion of a substrate can be alleviated by the organic buffer layer. In addition, since the gas barrier layer disposed on the top surface of the organic buffer layer is approximately flattened by approximately flattening the top surface of the organic buffer layer, portions on which stress is concentrated disappear from the gas barrier layer, thereby preventing the generation of crack.
When the organic buffer layer is thermally deformed (expanded or contracted), crack is generated in the gas barrier layer. Accordingly, there is a problem that the invasion of moisture from the outside cannot be completely prevented.